The present invention relates to a laser beam controller for surveying equipment, and particularly to a laser beam controller for surveying equipment which enables control of the quantity of the laser beam projected to a target.
Conventional surveying equipment using a laser beam generally comprises a laser beam oscillating medium 1 for emitting a laser beam, leading the laser beam emitted to a measurement target T and applying the laser beam to the target T; an irradiation optical system 10 comprising a mirror 2, an objective lens 3 and so on; and an observation optical system 20 comprising the objective lens 3, a focusing lens 4, an ocular 5 and so on for leading the laser beam reflected from the target T to an observer. Such an arrangement permits the observer to perform the predetermined surveying work while simultaneously observing the reflected laser beam spot and a cruciform index of a target graticule 6.
In such surveying equipment, when a large quantity of a laser beam is projected to the eyes of the observer, the observer perceives this and can prevent the incidence of the harmful laser beam on their eyes for a long time, thereby ensuring that their eyes are safe from any harm. In addition, in order to prevent the accidental incidence of the laser beam on the eyes or skin of a person other than the observer, a shutter 7 is provided on the radiation path of the laser beam so as to enable the observer operating the shutter 7 to cut off the laser beam when a danger is perceived.
In actual surveying work using the above-described surveying equipment, in a case involving a relatively small quantity of a laser beam and a short observation time, the safety of the eyes of the observer is maintained. As described above, however, it it necessary to observe the reflected laser beam spot for a relatively long time because the observer operates the surveying equipment while simultaneously observing the reflected laser beam spot and the cruciform index of the target graticule 6. When the observer observes the reflected laser beam spot which is not dazzling but has a relatively large quantity, the eyes of the observer are exposed to the harmful laser beam for a long time. Thus the observer's eyes are damaged or severely strained.
On the other hand, the quantity of the reflected laser beam is generally in inverse proportion to the second power of the distance between the surveying equipment used and the target and in proportion to the reflectance of the target when the quantity of the laser beam is constant. The quantity of the reflected laser beam thus varies within a wide range in the actual surveying work in which work the distance and the reflectance of the target widely varies depending upon the conditions for use of the surveying equipment. Particularly, in tunnel work in which a base rock is a target, because the reflectance of the base rock changes hourly , the quantity of the reflected laser beam also changes. This change in the quantity of the laser beam cannot be easily noticed by the observer who operates the surveying equipment while simultaneously observing the reflected laser beam spot and the cruciform index of the target graticule 6. There is thus a danger of the observer's eyes being damaged or severely strained.
Even if the above-described shutter 7 is provided for protecting the observer's eyes, since the shutter 7 is operated on the basis of decisions made by the observer, it is difficult to definitely ensure the safety of the eyes.
On the other hand, surveying work using the surveying equipment, which projects the laser beam, requires a sufficient quantity of reflected laser beam to be maintained to observe the laser beam spot. This is because the surveying work cannot be performed when the overall quantity of laser beam emitted from the laser beam oscillating medium 1 is reduced to a quantity insufficient for observation, when the reflectance of the target is decreased to a small value, or when the distance to the target is increased.
In the surveying equipment which projects the laser beam, survey accuracy is generally increased upon a decrease in the size of the laser beam spot observed. For example, when the surveying equipment is used as a pointer, as shown in FIG. 6, since the deviation d between both optical axes is decreased upon a decrease in the size of the laser beam spot observed, an adjustment can be made more precisely. In the case of an observation with the naked eye, a deviation of 1/8 to 1/10 of the laser beam spot size can be observed. This is true for a case where the present target is aimed at, a deviation from the present target is measured or a new target is established.
The size of the laser beam spot on the target T depends upon the illumination around the target T even if the intensity and the spread angle of the laser beam are constant. As shown in FIG. 7, the quantity of reflected laser beam and illumination around the target are shown on the ordinate, and the distance from the center of the laser beam spot is shown on the abscissa. In the drawing, the laser beam spot is shown as a curve 100. The diameter of the laser beam spot observed is AR, BR, CR at the levels AL, BL, CL, respectively, of illumination around the target. In the conventional surveying equipment, however, the observer cannot adjust the intensity of the laser beam projected to the target T and thus cannot set the laser beam spot to a desired size.